05000416/LER-2017-002

On March 24, 2017, it was determined that the A Standby Gas Treatment System (SGTS A) was not operating as expected. The investigation into the event revealed the Single Nest Power Supply had failed resulting in loss of flow control. It was determined the power supply had been replaced and the technical specification limiting condition for operation exited on February 23, 2017. The A SGTS was not run between replacement of the power supply and the time of discovery condition on March 24, 2017. Additionally, the B SGTS was removed from service for planned corrective and preventative maintenance on February 28, 2017 and returned to service on March 3, 2017. This condition prohibited by technical specifications in accordance with 10 CFR 50.73(a)(2)(i)(B) for the A SGTS train being inoperable for a period great than allowed by technical specifications. The cause of this event has been determined to be a power supply that could not be fully inserted due to pre-existing damage.

The damaged power supply was not appropriately corrected prior to installation due to an incorrect screening practice. The defective power supply was replaced and tested satisfactorily. Entergy established proceduralized barriers to minimize recurrence of similar errors through the establishment of pre-installation checks for the power supply as well as post maintenance testing of the replaced power supplies. There were no actual nuclear safety consequences or radiological consequences. No Technical Specification Safety Limits were violated.

(4-2017) to 366A U.S. NUCLEAR REGULATORY COMMISSION

Contents

CONTINUATION SHEET

(See NUREG-1022, R.3 for instruction and guidance for completing this form htiorAww.nrc.00vireadino-rrradoc-collectionsinureosistaff/sr1022,ra) APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-8001, or by e-mail to Infocollects.Resourcee nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Grand Gulf Nuclear Station, Unit 1 05000 416

DESCRIPTION

On March 24, 2017, while operating the A Standby Gas Treatment System (SGTS A) the SGTS Flow Recorder was indicated a downscale reading. The Plant Data System computer points indicated a flow mismatch between the available indications of approximately 5000 cubic feet per minute (CFM). Due to the mismatch indications and the downscale reading the surveillance was terminated and Standby Gas "A" was returned to standby.

The investigation of the identified conditions determined the failure of the systems was the Single Nest Power Supply. Failure of this power supply would result in a loss of the associated train's flow control. The investigation revealed that the power supply was replaced and the technical specification limiting condition for operation exited on February 23, 2017. The A SGTS was not run between replacement of the power supply and the time of discovery condition on March 24, 2017.

Prior to the power supply being replaced the system had been successfully tested and therefore it was determined that this condition could only have been present since the installation of the new Power Supply was completed on February 23, 2017.

The investigation further revealed that the B SGTS was removed from service for planned corrective and preventative maintenance on February 28, 2017 and returned to service on March 3, 2017.

The above described condition rendered the A SGTS inoperable and also resulted in a period when both SGTSs were inoperable during the same time period.

REPORTABILITY

The condition is also reportable as a condition prohibited by technical specifications in accordance with 10 CFR 50.73(a)(2)(i)(B) for the A SGTS train being inoperable for a period great than allowed by technical specifications.

An engineering evaluation was performed that demonstrated the SGTS A was able to perform its safety function with the identified nonconformance. Therefore this LER supplement retracts reporting this concern as a loss of safety function under 10 CFR 50.73(a)(2)(v)(C).

CAUSE

The cause of this event has been determined to be within the control system of the Single Nest Power Supply.

The equipment failure analysis determined the power supply could not be fully inserted due to pre-existing damage. The damage to the power supply was not appropriately corrected prior to installation due to an incorrect screening of the condition report that initially identified the pre-existing condition.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-2016) FiEnt, LICENSEE EVENT REPORT (LER) (A 2 CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http:ilwwwnrc.govireadina-rinidcc-collectionsinureasistaffisrl 022/0) APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infacollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Grand Gulf Nuclear Station, Unit 1 05000 416

3. LER NUMBER

CORRECTIVE ACTIONS

The defective power supply was replaced and tested satisfactory.

Proceduralized barriers were established to minimize recurrence of similar errors through the establishment of pre-installation checks for the power supply as well as post maintenance testing of the replaced power supplies.

The governance was reviewed as it relates to discovery of deficient conditions on replacement parts and required actions based on classification of the part (i.e. safety related, quality part, etc.). This action was performed to determine if this issue should have been identified as a NON CONFORMING part and if it should have been tagged and segregated. This review revealed the process was not followed and follow-up actions were developed to correct the cause of the error.

SAFETY SIGNIFICANCE

There were no actual nuclear safety consequences or radiological consequences as a result of this power supply failure. No Technical Specification Safety Limits were violated.

PREVIOUSLY SIMILAR EVENTS

The identified licensee event reports were reviewed and it has been determined that the causes and corrective actions for the previously identified events were sufficiently different that they could not have predicted or prevented the occurrence of this event.

LER-2017-002, Loss of Secondary Containment and Inoperability of the Standby Gas Treatment Systems as a result of a damages power supply.